The present invention relates to the structure of a cylindrical target to be applied to a magnetron sputtering apparatus (particularly, a direct-current magnetron sputtering apparatus) to be employed for forming a thin film, and its production method.
The magnetron sputtering method is known as one of techniques to form a thin film on a substrate of e.g. glass or plastic. JP-A-5-501587 discloses a sputtering system employing a rotating cylindrical target. This apparatus has a magnet inside the cylindrical target, and sputtering is carried out while the target is cooled from the inside and the target is rotated. The cylindrical target has advantages of a high efficiency of utilization and a high film-forming speed as compared with a flattened (planar type) target.
With respect to a production method of a cylindrical target, JP-A-5-214525 discloses a method of building up by a plasma spray method a target material as a film material to be sputtered, on the outer surface of a backing tube made of e.g. stainless steel or titanium. Further, there has also been known e.g. a method of disposing a target material formed to have a cylindrical shape, on the outer circumferential surface of a backing tube, and inserting a metal such as indium between both members to bond them, or a method of forming a one-piece body including the part of the backing tube by the target material.
However, in the case of the plasma spray method, there is a disadvantage that the target material or the backing tube material is limited by the compatibility (for example, the difference in heat expansion) between a material available for spraying and a material of backing tube. The method of bonding with e.g. indium requires a surface treatment to the outer circumferential surface of the backing tube and the inner circumferential surface of the target material. Further, a heating apparatus for melting and injecting the indium into the bonding portion, and a consideration to prevent the melted indium from leaking, are also required. Further, in a case where the target material is made of ceramics, the heat expansion rate of the target material is generally smaller than that of the backing tube made of metal or that of indium as a bonding material, whereby a problem that a gap is formed at the bonding portion due to a shrinkage difference at the time of cooling after the bonding, occurs.
Further, the target will be replaced when the target material is worn by sputtering. In a case of a target manufactured by a spray method or an indium bonding method, the separation of the backing tube from the target material is difficult and therefore, such a target is not suitable for reuse (recycling) of the backing tube.
On the other hand, although it is possible to form a one-piece body including the part of the backing tube by the target material, the structure of such one-piece type target does not have enough reliability because ceramics or some kinds of metal material have an insufficient strength, or a low durability to a mechanical impact. Further, there is a problem of manufacturing cost if the one-piece body is formed by an expensive target material.
The present invention has been made under consideration of such circumstances, and it is an object of the present invention to provide a cylindrical target which can broaden the possibility of selecting the target material and the backing tube material, which can simplify the manufacturing, and which can increase the capability of reuse (recycling), and to provide its manufacturing method.
In order to achieve the above object, the cylindrical target of the present invention is characterized in that a hollow cylindrical target material is disposed on the outer circumference of a cylindrical backing tube, and said backing tube and said target material are joined via a buffer material present between said backing tube and said target material.